Steroids in Germfree and Conventional Rats: 4. Identification and Bacterial Formation of 17α‐Pregnane Derivatives

Gas chromatography‐mass spectrometry was used to identify 3α‐hydroxy‐5α,17α‐pregnan‐20‐one, its 17β epimer and, tentatively, 3α‐hydroxy‐5α‐pregn‐16‐en‐20‐one in faeces from conventional rats. These steroids were present as conjugates having the chromatographic properties of sulphates. They could not be found in faeces from germfree rats. Incubations of 3β‐hydroxy‐pregna‐5,16‐dien‐20‐one and 3β,16α‐dihydroxy‐5α‐pregnan‐20‐one with intestinal microorganisms yielded as major products 3β‐hydroxy‐17α‐pregn‐5‐en‐20‐one and 3β‐hydroxy‐5α,17α‐pregnan‐20‐one, respectively. Smaller amounts of different isomers of these compounds were also obtained. It is suggested that the major pathway for the formation of 17α‐pregnane derivatives in the rat is a bacterial conversion of 16α‐hydroxylated precusors via aΔ¹⁶ intermediate.